This research exploits both quinacrine mustard fluorescence and electron microscopic methods for the following studies of chromosomes: (1) Electron microscopic studies of the Y chromosome in interphase - The fairly constant location of the interphase Y in nuclear projections in polymorphonuclear leukocytes means that the Y can be located under the electron microscope. The ultrastructural characteristics of these projections are being studied to discern the intrinsic structure of the interphase Y, and its relation to the nuclear membrane. (2) Fluorescene microscopic studies of secondary constrictions and satellites - Three experiments seek to determine whether satellite fluorescence is either related to nucleolar organizer activity, or inherited as a variant of chromosome structure: (A) Statistical studies in single tissues of relative number of fluorescent satellites and nucleoli; (B) Studies of the constrictions and satellites from wild-type, anucleolate and partial lethal nucleolate Xenopus laevis to see if deletions of the constriction affect satellite fluorescene; and (C) Studies of human populations to determine whether the frequencies of satellite fluorescent probes of human chromosome structure - Fluorescence studies of the interaction of several compounds with human chromosomes will determine whether any produce unique and informative patterns. (4) Y chromosomal aneuploidy in the community - Males are being screened by interphase fluorescene for Y aneuploidy, to determine its prevalence and to correlate psychosocial achievement with karyotype.